Thermoplastic pipes and valves are widely used in the chemical and petrochemical industries because of the ability of many thermoplastics to withstand prolonged exposure to caustic chemicals. Thermoplastics also tend to be less expensive and lighter than comparable metallic pipes and valves.
The chemical industry and the public have become increasingly aware of the potentially catastrophic effects of certain chemical spills or leaks. Many jurisdictions have enacted regulations and legislation intended to enhance the safety of the chemical industry and to minimize the possibility of leaks or spills. Additionally, high insurance rates and the possibility of liability in the event of a spill or leak have encouraged the chemical industry to consider technological improvements that will reduce the possibility of a leak.
Double pipes comprising an inner fluid carrying pipe and an outer pipe have been employed to achieve many objectives. Most typically, double pipes are used for heat insulation or heat exchange. However, double pipe systems have been used to prevent leaks or spills. Certain of these systems also have included detector means between the inner and outer pipes for sensing the occurrence of a leak. The detector means typically has comprised an electronic sensor that is operative to sense the presence of an electrically conductive liquid between the inner and outer pipes and to generate an appropriate signal to indicate the existence of a leak from the inner pipe.
One double-containment pipe system for thermoplastic pipes is shown in U.S. Pat. Ser. No. 4,157,194 which issued to Takahashi on June 5, 1979. More particularly, U.S. Pat. Ser. No. 4,157,194 shows a linear outer pipe that is formed with integral inwardly extending and radially aligned support ribs. An inner pipe is concentrically disposed within the outer pipe and is dimensioned to be supported on the ribs. The assembly of double-containment thermoplastic pipes shown in U.S. Pat. Ser. No. 4,157,194 further includes fittings which enable conversion to single pipes at elbow fittings, T-connections and such. The fittings of U.S. Pat. Ser. No. 4,157,194 include a pipe segment to mate with the linear inner fluid carrying pipe of the double-containment pipe system, and a flange which effectively seals off an end of the double-containment pipe section. Thus, the system shown in U.S. Pat. Ser. No. 4,157,194 includes double-containment pipes which extend along linear sections, but which do not extend through fittings. The double-containment pipes shown in U.S. Pat. Ser. No. 4,157,194 have several substantial deficiencies. In particular, the outer pipe with the integral inwardly extending flanges is difficult and very expensive to manufacture, and prevents the use of standard "off the shelf" pipes. Second, the system shown U.S. Pat. Ser. No. 4,157,194 does not provide for double-containment systems at the fittings at which leaks are quite likely to occur.
Another system of nested pipes is disclosed in U.S. Pat. Ser. No. 4,098,476 which shows a generally frustoconical member for supporting an inner tubular member concentrically within an outer tubular member for use in a cold optics system which requires a telescope to be supported inside an evacuated housing. The frustoconical support must be slid longitudinally over the inner tubular member.
Many dual pipe systems have been developed to insulate stove pipes and such. Examples of these pipes are shown in U.S. Pat. Ser. No. 2,650,112 which issued to Kinkead on Aug. 25, 1953; U.S. Pat. Ser. No. 2,756,032 which issued to Dowell on July 24, 1956; and U.S. Pat. Ser. No. 3,847,208 which issued to Ollendorf on Nov. 12, 1974.
Other double-containment pipes are shown in U.S. Pat. Ser. No. 4,182,378 which issued to Dieter on Jan. 8, 1980 (oil pipe); U.S. Pat. Ser. No. 3,899,007 which issued to Miller on Aug. 12, 1975 (underground high temperature conduit); U.S. Pat. Ser. No. 2,860,311 which issued to Balian on Nov. 11, 1958 (wave guide); U.S. Pat. Ser. No. 4,095,041 which issued to Netzel on June 13, 1978 (gas insulated transmission line cable); U.S. Pat. Ser. No. 4,250,927 which issued to Newburg on Feb. 17, 1981 (aircraft ducts); U.S. Pat. Ser. No. 4,280,535 which issued to Willis on July 28, 1981 (drill pipe); U.S. Pat. Ser. No. 4,397,308 which issued to Villain on Aug. 9, 1983 (solar sensor) and U.S. Pat. Ser. No. 4,250,928 which issued to Nishikawa on Feb. 17, 1981.
Still other devices are known for connecting multilayer pipes. For example, U.S. Pat. Ser. No. 4,573,527 issued to McDonough on Mar. 4, 1986 and shows a complex connecting member for joining the pipes of a heat exchanger. U.S. Pat. Ser. No. 4,400,019 issued to Fruck on Aug. 23, 1983 and shows a connector for joining multilayer pipes which comprise an inner plastic pipe, an outer steel casing and a cement grout mixture therebetween. U.S. Pat. Ser. No. 4,345,785 issued to Bradford on Aug. 24, 1982 and shows a connector for an insulated pipe, while U.S. Pat. Ser. No. 4,184,702 issued to Morris on Jan. 22, 1980 and shows a connection for certain plumbing fixtures.
The extensive prior art work on double pipe systems generally does not show efficient systems for thermoplastic pipes that can be used with stock pipe items and that can be readily assembled in the field by personnel with little special training.
Accordingly, it is an object of the subject invention to provide a double-containment pipe assembly that can employ available thermoplastic pipes.
It is another object of the subject invention to provide a double-containment pipe assembly that can be readily assembled in the field to meet the demands of any particular pipe system.
A further object of the subject invention is to provide a double-containment pipe system that can provide double-containment protection through fittings.
An additional object of the subject invention is to provide a double-containment pipe system that can accommodate and control thermal expansion along the length of the pipe.
Still a further object of the subject invention is to provide a double-containment pipe system that is well suited to use with electronic sensing systems for sensing the presence of a leak.